The present invention relates to a device for excavating an elongate depression in soil, especially for excavating a ditch, wherein the device comprises at least one motor for driving milling tools which are substantially in the shape of a cone or frusto-cone and are supported so as to be driven in rotation about their longitudinal axis. The longitudinal axes of the milling tools extend at an angle to one another, and the mantle surfaces of the milling tools are positioned at one location of their circumference with a minimal spacing to one another that provides a working play. The thus arranged milling tools provide a continuous working plane.
For excavating a ditch, for example, for the purpose of laying pipelines in the soil, it is conventional to employ excavators depending on the desired width of the ditch, have a correspondingly wide excavator shovel. Depending on the type of soil, it is expedient to first loosen the soil so that the excavator shovel can easily remove the soil. Known ditch milling devices have, in general two, driven milling tools which extend laterally from a central support and are driven in rotation about their longitudinal axis. This construction requires a stay of the support to be positioned between the milling tools so that during milling a strip of soil will not be loosened which corresponds to the stay between the milling tools. Thus, a nonuniform milling result will be obtained. For removing the strip of soil that remains at the center, the milling device is then moved back and forth in a direction transverse to the longitudinal direction of the ditch which results in the ditch being made wider than is actually necessary. This back and forth movement results in an increased loading of the excavator due to transverse forces which act on the support of the excavator arm.
In European patent application 0 253 726 a device for excavating an elongate depression in the soil, especially for excavating a ditch, is known which comprises semi drums driven by a motor which are provided at their circumference with tools. The semi-drums are supported on a vertical stay which is positioned between the semi-drums. The rotational axis of the semi-drums are slightly slanted in a downward direction. As a drive a hydraulic motor is used.
It is an object of the present invention to provide a device of the aforementioned kind which is optimized with respect to the revolving masses of the milling tools and which during operation is directionally stable.